The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is propelled by one or several propulsion assemblies each comprising a turbine engine housed in a tubular nacelle. Each propulsion assembly is fastened to the aircraft by a mast usually located under or on a wing or at the fuselage.
A nacelle usually has a structure comprising an air inlet upstream of the motor, a median section intended to surround a fan or the compressors of the turbine engine and its casing, a downstream section able to accommodate thrust reversal means and intended to surround the combustion chamber of the turbine engine, and is usually terminated by an ejection nozzle of which the exit is located downstream of the turbine engine.
Generally, the turbine engine comprises a system of blades (compressor and possibly fan or non-shrouded propeller) driven in rotation by a gas generator through an assembly of transmission means.
A system for distributing lubricant is provided to provide a good lubrication of these transmission means and to cool them.
As a result, the lubricant must then also be cooled by means of a heat exchanger.
To this end, a first known method consists in cooling the lubricant by circulating through an air/oil exchanger using the air collected in a secondary vein (called cold flow) of the nacelle or in one of the first stages of the compressor.
The collection and circulation of air through this exchanger, disrupts the stream of air flow and causes additional head losses (drag) which is not desirable.
It has in particular, been calculated that in the case of a fan motor with reducer, it could represent losses equivalent to around 1% of fuel consumption.
Another solution has appeared within the context of nacelle anti-icing systems.
In fact, in flight, according to the conditions of temperature and humidity, ice may form on the nacelle, in particular at the outer surface of the air inlet lip equipping the air inlet section.
The presence of ice or frost modifies the aerodynamic properties of the air inlet and disrupts the movement of the air towards the fan. Moreover, the forming of frost on the air inlet of the nacelle and the ingestion of ice by the motor in the event of separation of ice blocks may damage the motor or the airfoil, and pose a threat to flight safety.
A solution to device the outer surface of the nacelle consists in preventing ice from forming on this outer surface by maintaining the concerned surface at sufficient temperature.
Thus, the heat of the lubricant may be used to heat the outer surfaces of the nacelle, the lubricant being as a result cooled and able to be re-sued in the lubrication circuit.
Documents U.S. Pat. No. 4,782,658 and EP 1 479 889, in particular, describe the implementation of such anti-icing systems using the heat from the motor lubricant.
More specifically, document U.S. Pat. No. 4,782,658 describes an anti-icing system using outside air collected by a scoop and heated through an air/oil exchanger to help with the de-icing. Such a system allows a better control of the exchanged thermal energies, but the presence of scoops in the outer surface of the nacelle causes a loss in aerodynamic performances.
Document EP 1 479 889 itself describes, an anti-icing system of an air inlet structure of turbojet engine nacelle using a closed circuit air/oil exchanger, the heated internal air of the air inlet structure being put in forced convection by a ventilator.
It is worth noting that the air inlet structure is hollow and forms a closed chamber of de-icing air circulation heated by the exchanger disposed inside this chamber.
Thus, the thermal energy available for the de-icing depends on the temperature of the lubricant.
Furthermore, the exchange surface of the air inlet structure is stationary and limited and the actually dissipated energy substantially depends on the heat required for de-icing and hence on external conditions.
It ensues that the cooling of the lubricant, as well as the temperature at which the air inlet is maintained, are difficult to control.
As is noted, the proposed systems are difficult to adjust depending on the quantity of heat to be dissipated and the actual de-icing needs and are not suitable according to the actual needs and in particular the flight phases. Moreover, the outer surface of the lip alone may not be enough to dissipate all the heat conducted by the lubricant, particularly if the turbine engine is equipped with a reducer which dissipates a large quantity of heat.
Hence, there is a need for a system which allows controlling and optimizing both the cooling performances of the motor lubricant and the de-icing performances.